Southern Ocean cloud and aerosol data: a compilation of measurements from the 2018 Southern Ocean Ross Sea Marine Ecosystems and Environment voyage

Abstract

Abstract. Due to its remote location and extreme weather conditions, atmospheric in situ measurements are rare in the Southern Ocean. As a result, aerosol–cloud interactions in this region are poorly understood and remain a major source of uncertainty in climate models. This, in turn, contributes substantially to persistent biases in climate model simulations such as the well-known positive shortwave radiation bias at the surface, as well as biases in numerical weather prediction models and reanalyses. It has been shown in previous studies that in situ and ground-based remote sensing measurements across the Southern Ocean are critical for complementing satellite data sets due to the importance of boundary layer and low-level cloud processes. These processes are poorly sampled by satellite-based measurements and are often obscured by multiple overlying cloud layers. Satellite measurements also do not constrain the aerosol–cloud processes very well with imprecise estimation of cloud condensation nuclei. In this work, we present a comprehensive set of ship-based aerosol and meteorological observations collected on the 6-week Southern Ocean Ross Sea Marine Ecosystem and Environment voyage (TAN1802) voyage of RV Tangaroa across the Southern Ocean, from Wellington, New Zealand, to the Ross Sea, Antarctica. The voyage was carried out from 8 February to 21 March 2018. Many distinct, but contemporaneous, data sets were collected throughout the voyage. The compiled data sets include measurements from a range of instruments, such as (i) meteorological conditions at the sea surface and profile measurements; (ii) the size and concentration of particles; (iii) trace gases dissolved in the ocean surface such as dimethyl sulfide and carbonyl sulfide; (iv) and remotely sensed observations of low clouds. Here, we describe the voyage, the instruments, and data processing, and provide a brief overview of some of the data products available. We encourage the scientific community to use these measurements for further analysis and model evaluation studies, in particular, for studies of Southern Ocean clouds, aerosol, and their interaction. The data sets presented in this study are publicly available at https://doi.org/10.5281/zenodo.4060237 (Kremser et al., 2020).

Observations and Modeling of Rime Splintering in Southern Ocean Cumuli

“…Vignon et al (2021) showed that immersion freezing INP measurements collected with filters exposed for 24-48 hr from a ship platform located near the Mawson Antarctic coastal station suggest a log-linear extrapolation with a different slope in the temperature regime of interest here, resulting in 10 −5 L −1 as an upper bound for INP concentrations within the rime-splintering temperature zone. Spectra of INP from filters exposed for 24 hr aboard the RV Tangaroa at 50-80°S, which had limits of detection near −15°C (Kremser et al, 2021), suggest an INP concentration of 10 −5 L −1 at −13°C, matching the concentrations predicted in the extrapolation in Figure 4. Regardless, all these estimates suggest that the observed ice should have very low number concentrations if primary nucleation alone is active.…”

DMS cycling in the Sea Surface Microlayer in the South West Pacific: 1. Enrichment potential determined using a novel sampler

“…The atmospheric DMS concentration [𝐷𝑀𝑆] 𝑎𝑡𝑚 was neglected as this is several orders of magnitude lower than the dissolved DMS concentration (Kremser et al, 2021). Flux estimates were obtained using DMS concentrations from three different depths: FSML corresponds to DMS air-sea flux calculated using DMS concentration in the SML, FSSW to DMS concentration in the SSW, and F5 m to DMS concentration at 5 m depth from the CTD.…”

Classification of the Below-Cloud Mixing State Over the Southern Ocean Using In-Situ and Remotely-Sensed Measurements

“…via 40 m of conductive hose. Within the laboratory, a passive cavity aerosol spectrometer probe (PCASP-100X; Droplet Measurement Technologies) and a differential mobility particle sizer (DMPS, TSI) mea-sured the ambient concentration of particles suspended in the atmosphere (Kremser et al, 2020). The PCASP measured the number concentration size spectra of particles suspended in the boundary layer in 30 size bins (0.1-3.0 µm) every minute.…”

“…When data from the DMPS were not available, measurements from the PCASP were used to constrain the abundance and size of accumulation mode particles. Further details on sampling set-up and analysis, including correction factors for losses through the sampling line and methods for handling contamination from ship exhaust, are described in Hartery et al (2020) and Kremser et al (2020). In parallel to the size-resolved particle concentration spectra generated by the SMPS and PCASP, the total number of cloud condensation nuclei (CCN) was measured using a CCN counter (CCNC-100; Droplet Measurement Technologies).…”

“…By contrast, ship-based measurements can be made in nearly all conditions. Here, we use measurements on the R/V Tangaroa during a voyage to the Ross Sea in the austral summer of 2018 to establish conditions in which particles near the surface are turbulently mixed to cloud base (Kremser et al, 2020). Establishing conditions when sea-level measurements are relevant to cloud will enable future research to better exploit sea-level measurements in aerosol-cloud interaction studies, and adds value to the growing catalogue of near-surface measurements available from recent voyages.…”